Skip to main content

Full text of "Soft Circuits"

See other formats

LED Tank Top 

Make] Projects 

hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat* 

build, hack, tweak, share, discover,- 

LED Tank Top 

Written By: Leah Buechley 


Fabric marker (1) 
Multimeter (1) 
Scissors (1) 
Sew No More (1) 
Sewing machine (1) 
Sewing needle (1) 
Soldering iron (1) 
T-square (1) 


Thread (1) 


Liquid stitch (1) 

AVRmega15 microcontroller (1) 

DC power supply (1) 

Serial adapter (1) 

Battery holder (1) 

On/off switch (1) 

AVR programmer (1) 

Lead-free solder (1) 

Crimping beads (1) 

about twice as many as LEDs 

Garment (1) 

or a piece of fabric and a pattern to 

make your own 


I built this shirt to experiment with wearable computing and electronic textile technology and 
© Make Projects Page 1 of 16 

LED Tank Top 

realized along the way that the basic materials were actually quite easy to work with and 
there was lots of room for creativity and innovation at all levels, so I was inspired to write up 
this do-it-yourself guide. Everyone should be playing with this stuff! It's great fun for geeks 
and divas — build yourself a sparkly fashion accessory and program it with the Game of Life 
or other hacker animations. You're guaranteed to turn heads whenever you're out on the 

Step 1 — Gather your materials. 

# Here's an overview of all the 
materials and tools you'll need. 

• Clear a work space and stay 

Step 2 — Design your display. 

• Decide on the number of LEDs you want and their general placement. This will depend on 
the garment you chose as well as how you'd like the display to look. 

• I decided to sew a simple tank top, and I chose to place the LEDs evenly across my tank 
top every 2". Since my tank top is approximately 28" around and 12" tall, I needed 84 

© Make Projects 

Page 2 of 1 6 

LED Tank Top 

Step 3 — Make sequins with your beads and LEDs. 



• Get out the crimping beads and surface mount LEDs. 

• Using a soldering iron with a very clean tip, place the tip of the iron into a bead. Melt some 
solder onto the outside of the bead. With the soldering iron, drag the bead up to the LED. 

• When the melted solder touches the LED's contact, the bead will adhere to the LED. Lift 
the soldering iron out of the bead. 

• At this stage, you may want to take some measures to distinguish the cathode lead (-) 
from the anode lead (+) of each LED. 

• The cathode end is often marked with a green line on the front or back of the 
surface mount package. To distinguish the two, you can solder a brass crimping 
bead to the cathode lead and a silver bead to the anode lead for each LED. 

• TIP: If your soldering iron tip is dirty, it will stick to the bead and make the job very 
difficult. If this is happening, you should clean or replace your tip. Once you get the 
hang of it, this should go pretty fast. You should be able to solder 100 LEDs within an hour. 

© Make Projects 

Page 3 of 16 

LED Tank Top 

Step 4 

• In a similar way, solder beads to 
the appropriate leads for your 
battery and switch, so that they 
can also be sewn on. 

• This is the switch sequin. 

© Make Projects 

Page 4 of 1 6 

LED Tank Top 

Step 5 — Sew your LED matrix. 

• With a marking pen, mark the lines 
for your LED pattern on the 

• Also, mark where you want your 
microcontroller (IC socket) and 
power supply to be. 

• You want a grid of 
conductive traces where the 
vertical traces do not touch the 
horizontal ones. A simple way to do 
this is to put one trace on one side 
of the fabric and the other trace on 
the flip side of the fabric, utilizing 
the fabric as a natural insulator. 
The lines for the vertical traces 
should be on one side of your 
garment, and the lines for the 
horizontal traces should be on the 

• I marked both sets of lines on both 
sides of my tank top to make sure 
my lines were well placed. Use a 
T-square to get good right angles 
and straight lines. 

© Make Projects 

Page 5 of 1 6 

LED Tank Top 

Step 6 

• Make a bobbin of silver-coated 
thread for your sewing machine, 
and put it in the machine. Use a 
spool of ordinary thread for the top 

• Using silver-coated thread 
in the bobbin of a sewing 
machine will allow you to sew 
conductive horizontal traces on one 
side of your garment and 
conductive vertical traces on the 
other side. As you sew, the bobbin 
thread will remain on the underside 
of the fabric you are sewing. 

© Make Projects 

Page 6 of 1 6 

LED Tank Top 

Step 7 

• Sew one trial row-column crossing, 
and use the multimeter to make 
sure your threads are being 
sufficiently insulated by the fabric. 
If your fabric is too thin, the bobbin 
thread may be pulled through the 
fabric, and your crossing traces 
may short out. 

• If there is contact at your 
intersections, you will need to take 
action to correct this. As you are 
sewing out the traces, you should 
stop the sewing machine just 
before each intersection, and, 
without breaking the threads, move 
your fabric past the intersection 
and resume sewing. This will 
ensure that the silver-coated thread 
stays on the proper side of the 
fabric at each crossing. 

© Make Projects 

Page 7 of 1 6 

LED Tank Top 

Step 8 


1 1 PI M 

• Sew out your vertical traces. Flip your garment over and sew out your horizontal traces. 

• Sew one trial row-column crossing, and use the multimeter to make sure your threads are 
being sufficiently insulated by the fabric. If your fabric is too thin, the bobbin thread may be 
pulled through the fabric, and your crossing traces may short out. 

• You should stop your pattern stitches a few inches from the IC socket to leave room for 
the knots you will make when sewing the socket on by hand. 

• Here are the top and bottom views of my partially assembled tank top after I sewed on my 

Step 9 — Prepare and sew on the IC socket. 

• Before you start sewing threads onto the IC socket, you should familiarize yourself with 
the pins of the microcontroller. Here's the pin layout diagram for the ATmega16 chip. 

• All the pins labeled PA0-PA7, PB0-PB7, PC0-PC7, and PD0-PD7 are general-purpose 
input/output pins that can be used to power LEDs and the like. See my sample code and 
header files to see how to reference and control individual pins with your code. 

© Make Projects 

Page 8 of 1 6 

LED Tank Top 

Step 10 

• Trim the pins off the bottom of the socket and pull off any tape or other material blocking 
the holes. If necessary, drill out the holes so that a needle can pass through them. Position 
the socket where you want it on your garment and stitch it in place with silver-coated 
thread, sewing traces from each microcontroller socket to the pattern traces you sewed. 

# You want to make sure that the silver-coated thread makes contact with each 
socket hole, but also be careful that no two threads cross. This is a delicate job that 
requires some patience, but if you're used to doing soldering or any other meticulous work, 
it should be no problem. 


Step 11 

• Make sure that you tie your knots 
where there is ample room for them 
(away from the socket) and where 
they're less likely to cause shorts 
with neighboring traces. Coat each 
knot with fabric glue. This will keep 
knots from fraying and coming 

© Make Projects 

Page 9 of 1 6 

LED Tank Top 

Step 12 — What is a short? 

• A short or "short circuit" occurs when the positive terminal of a power supply is 
connected directly to the negative terminal of a power supply. On your shirt, if two 
neighboring traces are touching while one of them is high (positive) and the other is low 
(negative), a short circuit is created. This kind of short circuit will prevent your LEDs 
from lighting up and is likely to cause your microcontroller to overheat and eventually 
die. Short circuits in more high-powered applications can cause fires and explosions. 

© Make Projects 

Page 10 of 16 

LED Tank Top 

Step 13 

• Attach the cathode end of each 
LED to a row, and the anode end of 
each LED to a column (or vice 
versa). If you did not take steps 
during the soldering phase to 
differentiate the cathode from 
anode leads, you will have to make 
the distinction now. 

• The cathode end of the LED is 
often marked with a green line on 
the front or back of the surface 
mount package. If you are able to 
find this marking despite your 
soldering, you can use it. 
Otherwise, learn to distinguish the 
direction from the appearance of 
the face of the LED. Test one by 
running a current through it for 
reference. Be careful to use a 
voltage and current appropriate for 
your LED. 

© Make Projects 

Page 11 of 16 

LED Tank Top 

Step 14 

• While sewing, take care to make 
good connections between your 
thread and each bead, looping the 
thread through each bead several 
times, as shown here. 

• The fastest way to sew is to 
stitch each row and column 
continuously, not stopping to tie off 
the thread for each LED. In other 
words, sew in the cathode end of 
one LED, and sew down your row 
to the next LED cathode without 
cutting your thread. 

• However, this makes 
replacing badly sewn or 
broken LEDs harder, since you'll 
have to cut the continuous thread 
and tie the ends off in the event of 
a problem. Alternatively, you can 
sew each LED on individually. This 
will make repairs easier, but your 
sewing will take much longer. I 
chose the first option for faster 
sewing, but I did have to replace a 
few LEDS. 

© Make Projects 

Page 12 of 16 

LED Tank Top 

Step 15 — Test your circuit. 

• Using a multimeter, make sure 
none of your traces are shorting 
out with one another, and all of 
them are leading to the appropriate 
LED rows and columns. Silver- 
coated thread tends to fray and 
give off small "hairs." 

• Make sure there are no miniscule 
conducting hairs interfering with 
any of your traces. 

Step 16 

• You may also want to make sure 
your LED pattern is working 
properly by attaching the leads of 
your power supply to the rows and 
columns of your pattern in turn. 
Look at the specifications that 
came with your LEDs if you're not 
sure what power supply to use or 
you may fry all of your LEDs! My 
multimeter (in beep mode) doubles 
as a low-current power supply, 
illuminating an LED when its leads 
are attached to the right threads. 

© Make Projects 

Page 13 of 16 

LED Tank Top 

Step 17 

• Once you've done some thorough 
testing, glue an insulating backing 
onto the traces you sewed for your 
IC socket, so that your power 
supply will be easy to attach and 
these traces will remain in place 
without fraying with wear. 

Step 18 — Attach the power supply and switch. 

• Sew the switch and power supply 
to the garment. 

© Make Projects 

Page 14 of 16 

LED Tank Top 

Step 19 

# Glue an insulating backing over your power supply and switch traces so that you will not 
accidentally turn on your display. 

• Here is the inside view of my tank top after I sewed on the power supply. Notice the 
insulating backing that was applied prior to sewing. 

Step 20 — Program the controller. 


• Download the code for the "Game of Life" along with software to compile the program on 
your PC and connect to and download the program to the AVR microcontroller. 

• A British mathematician named John Horton Conway invented the "Game of Life" in 
1970 as a way to simulate cell-based birth, reproduction, and death based on 
simple rules. Wikipedia has an excellent article about The Game of Life . 

• Follow the instructions for installing the software and setting it up to program the controller 
at LED Tank Top Code Install . 

© Make Projects 

Page 15 of 16 

LED Tank Top 

This project first appeared in CRAFT Volume 01 . 

This document was last generated on 201 2-1 1-03 11:11:15 PM. 

© Make Projects Page 1 6 of 1 6